Porous electrode for a fuel cell and method of making same

ABSTRACT

A porous electrode for a fuel cell comprising a catalytic layer comprised of a mixture of active carbon and teflon, a stop layer comprised of teflon deposited on the catalytic layer, and current collector means including a grid compressed on the two preceding layers, so that it crosses through the stop layer and penetrates into a part of the thickness of the catalytic layer. The electrode has a porosity in the order of 50%.

[451 Aug. 12, 1975 1 POROUS ELECTRODE FOR A FUEL CELL References Cited UNITED STATES PATENTS AND METHOD OF MAKING SAME Inventors: Pierre Groult, Longj umeau;

l36/120 FC 136/86 D 136/86 D 3,442,715 5/1969 Yee et al. 3,520,730 7/1970 Puffer 3,660,165 5/1972 Francois Hubert, Paris; Jacques Daunay, Versailles; Pierre Bono, Morangis, all of Ftafic e 1 Primary Examiner John H. Mack [73]- Assignee. Soclete Generale de Constructions Assistant Examinerv H: A. Feeey Eleciriques et l' Alsthom Attorney, Agent, or FirmCraig & Antonelli & Cte, France Jan. 24, 1974 [57] ABSTRACT A porous electrode "for a fuel cell comprising a cata- [22] Filed:

[21] Appl. No.: 436,330

lytic layer comprised of a mixture of active carbon and teflon, a stop layer comprised of teflon deposited on the catalytic layer, and current collector means in- [30] Foreign Application Priority Data Jan, 24, ,&r;..4.-.-..-.......,.

France eluding a grid compressed on the two preceding layers, so that it crosses through the stop layer and pene- L e V. o 7 .m v 5 f mo m 0 mm e h $t mm k Fm mm mwp fa mh m 0 on c .m 6 e U 0 D R 6 8 8 m 3mD l 6 .90 0 CH F "0 1 WW 1 "3 "Mr m m I d d 5mm UIF 23 claims, 3 Drawing Figures PATENTED AUGI 2-1975 POROUS ELECTRODE FOR AEUEL mp" METHOD OF MAKTNG' SAME.

The present invention concerns a porous electrode for a fuel cell and more particularly a icell using 'liqwith an electrolyte containing a fuel .in the-dissolved state, whereas the other face is in contact with'a combustive, are known. Current c olle ctorsare arranged in contact with the faces andprovide forthe directing of the ions resulting from the electrochemical process. I

"about 35O to about-420C. maint'ai ned. from about 5 to 3 other characteristics and advantages of the invention Such electrodes have, nevertheles s, a certain nurribe r of disadvantages and more particularly it i s neces'sary to implement thedisadvantages of gaseous combustives at high pressures. Moreover, such electrodesliave low potentials with values that are. very far from the optimum values and that which, for a given electrolyte, correspondto the maximum performanceof thestorage cell as a whole. I

The present invention enables be overcome and it has for its object a porous electrode having interesting characteristics, particularly from the conductivity and potential point of vview of the electrode, which is easy to produce and has a moderate cost. i

The invention therefore has as it s'aim a porous electrode for a fuel cell comprising:-

a catalytic layer comprised of a mixture of a catalyst and of a polymer, more particularly polytetraflu- Orethylene;

a layer called a stop layer arranged on one of. the

such disadvantages to" ventionfa'nd' FIGS. 221 and 2b illustrate the" implementing of the method ventio willb e'come apparentfrorn the" foilowing description, vi y. Pit-a P QEiUPSWfiUg e am a g 6 limiting charaeter, with referencef'tothe accompanying drawings and diagrams, inltyhichi FIGQ'I shows'aporous ele'fctrod for producing an electrode accordingto the inltriiust "beiniderstood that in these figures; the thickness of the various layers has-purposely beeen exag- Wit hreference'to FIG. 1, ajporou's electrode accord- :ing' to the invention comprises" a porous catalytical layer 1.'cdnsiimredbys am-r of active carbon and -o'f;'polytetrafludrethylene' (PT-FE) in proportions of 'abdiir- 40 its about "90% by weightand of about'6O to about l0% by weight respectively. On layer 1 is ar- A ranged a layer 2 c a lled; the stop layer, also consisting of current collector means 3, 'consisting for example of a grid or expanded metaljfelement made of nickel or stainless steel is interlaced with the layers 1 an 2 as shown. metal cathode collector 4 (made of a metal such as nickel or stainless steel) for providing Ifthe electric connection with th e neighboring electr ode faces of the catalytic layer and made of saidpolymer,

a current collector means including a grid madeof an electronically conductive material 'anda chemically inert material; and

a separator means comprised layer arranged on the other face of-thecatalytic layer;

that electrode being characterized-in that.- the said current collector crosses through thewhole o'f the'stop layer and penetrates into apart of the thickness of. said catalytic layer. l l

The invention concerns also a method forproducing a porous electrode in which, successively;

a mixture of catalyst such ascarbon in: a proportion by weight between about 40-and about 90% a'nd polytetrafluorethylene in a proportion by'weight between about 10 and about 60% previously dispersed in dibutylphthalate or thelike, is depositedona sheetof aluminum; i

a part drying of the deposit, is

a stop layer of polytetrafluorethylane previously-dis compressed at a pressure comprised between about 500 and about 2,500 kg/sq. cm.; and

a sintering of the assembly of layers by heating in a neutral or reducing atmosphere to a temperature of of a fibrous tissue or -the; direction of the arrow F with methanol and an elec- (not shown) hasjalso beenshown, it being understood thattheelectrode described forms'a part of an assembly of bipolar electrodes constituting the fuel cellls uch a compact assembly being of the filter-press type Against-the other face of the layer 1 is arranged a ,separator s consisting of an airy tissue of fibers such as regenerated cellulose or asbestos; whereas another metai; collector 6 including a catalytic layer provides the connection with another neighboring electrode (not shown). I I

Oneof the faces-ofttheelectrode thus shown is fed in I trolyte consisting-of a potassium hydroxide or an alka- .-line carbonate solution, whereasthe other face is fed ,within the direction of the arrow F' with air.

'-. F:lGS. ,2a and. 212 illustrate further vthe implementing of the method for producin'ga porous electrode according to the inyerttion.

. According to BIG. 2a, the catalytic layer is deposited in the first instance on a sheet of aluminum 8, using awell known serigraphi'cmethod, keeping the deposit zto a determined thickness. For'that purpose the, active carbon andthe.arepreviously dispersed in dibutylphthalate, water orthe l ike liquid diluent, so as to -obtain an oily ink. After, partialjdrying,aqporous layer 1., on. which 7 is; depositednhe stop laye r 1 2 by. a similar -technique; is obtained After, furthe drying, the ex- .=.panded metalpart 3 is. arranged onethe assembly as shown, then the" assembly issubjected-to a pressure of 1,900 kg/sq cmf, indicated by the arrows F .:F1G. 2b shows that such a pressure has the effect of making the expanded metalpartipenetrate inside-ithe whole of the thickness of the stop layer 2 like a punch tool and inside-a fractionlpr portion-ofltliethickness of the catalytic layer.l, as shown; thus providing an excellent electric contact. Such apressure has, moreover, the effect of releasing the aluminum sheet 8. To great advantage, a lubricant such as a fluocarbonated oil which makes the sliding of the layersinto the gaps in the expanded according to 3 metal part 3 easier, may be incorporated in the inks used for forming the layers 1 and 2.

Subsequent to that compression phase of the method, a sintering of the assembly is effected in a neutral or reducing atmosphere consisting of nitrogen or a mixture of nitrogen and hydrogen at a temperature in the order of 380C. for 30 minutes.

An electrode having approximately an overall thickness of 100 to 200 microns, a porosity of 50% and a conductivity of 0.2 to 0.1 (OX cm) for the catalytic layer is thus obtained.

The electrodes thus produced may be installed as previously described to constitute a filter-press type cell.

it must be understood that this further assembly will be effected providing for the separators 5 as we'll asfor the collectors 4 and 6 (FIG. 1).

It will be observed, moreover that such a porous electrode makes it possible to feed the cell with air at a pressure of a few millibars; it being very easy to do this by means of a simple fan.

It will also be observed that the stop layer 2 prevents the methanol from crossing through the electrode and evaporating, the temperature of the assembly being in the order of 75C.

It must be understood that the invention is in no way limited to the embodiment described and illustrated, which has been given only by way of an example.

More particularly, without going beyond the scope of the invention, details may be modified, certain arrangements may be changed or certain means may be replaced by equivalent means.

What is claimed is:

l. A porous electrode for a fuel cell comprising:

a catalytic layer containing a mixture of a catalyst and of a polymer;

a stop layer arranged on one of the faces of the cata lytic layer and consisting essentially of said polymer, the stop layer and the catalytic layer having an open porosity of from about 40 to about 60%; and

current collector means made of an electronically conductive and chemically inert material;

said electrode being characterized in that the current collector means crosses through portions of the whole of the stop layer and penetrates into portions of the catalytic layer.

2. The electrode of claim 1, further comprising a separator layer comprising a fibrous tissue arranged on the other face of the catalytic layer.

3. The electrode of claim 1, wherein said current collector means is a reticulated member having a plurality of interconnected portions that extend through said stop layer into said catalytic layer.

4. The electrode of claim 1, wherein said collector means is a metallic grid having a plurality of elements spaced from each other in a predetermined pattern that extend through said stop layer into said catalytic layer.

5. The electrode of claim 4, wherein said grid is made of two sets of parallel extending metallic elements, which intersect each other.

6. The electrode of claim 4, wherein the grid is made of nickel or stainless steel.

7. The electrode of claim 1, wherein the polymer is a polyfluorinated polyolefin.

8. The electrode of claim 1, wherein the catalyst is powdered active carbon and said polymer is polytetrafluorethylene.

9. The electrode of claim 1, wherein the collector means penetrates into said catalytic layer with an outer surface that is level with and that forms a portion of an outer surface of one face of the electrode and an inner surface that contacts portions of the stop layer disposed within said electrode, other portions of said stop layer forming the remaining portions of the outer surface of said one face of the electrode.

10. The electrode of claim 1, wherein the catalytic layer is a sintered porous member.

11. A method for preparing a porous electrode for a fuel cell which comprises:

a. depositing a mixture of a catalyst in a proportion by weight comprised between about and about 40% and of a polymer in a proportion by weight comprised between about 10 and about 60%, dispersed in a liquid volatile diluent, on a metal sheet;

b. partial drying the deposit;

c. depositing a stop layer consisting essentially of said polymer diluted in the liquid diluent on the catalytic layer;

d. drying of the stop layer;

e. arranging a current collector means on the stop layer and compressing the collector means at a pressure from about 500 to about 2,500 kg/sq. cm to form an assembly of layers and collector means; and

f. sintering of the assembly by heating at an elevated temperature.

12. The method of claim 11, wherein the catalyst is active carbon and the polymer is a polyfluorinated polyolefin.

13. The method of claim 12, wherein the polymer is .polytetrafluorethylene.

14. The method of claim 13, wherein the assembly is sintered in a neutral or reducing atmosphere at a tem perature of from about 350C. to about 420C. for about 5 to about 60 minutes.

15. The method of claim 11, wherein said diluent is dibutylphthalate.

16. The method of claim 11, wherein a lubricant is used jointly with the diluent.

17. The method of claim 16, wherein the lubricant is a fluorocarbon oil.

18. The method of claim 1, wherein the metal sheet is aluminum.

19. An electrochemical storage cell comprising at least one electrode according to claim 1.

20. The electrode of claim 1, wherein the stop layer consists of polytetrafluorethylene.

21. The electrode of claim 1, wherein the stop layer is freeof catalyst.

22. A method of claim 11, wherein said stop layer consists of polytetrafluorethylene diluted in dibutylphthalate.

23. The method of claim 11, wherein the stop layer is free of catalyst. 

1. A POROUS ELECTRODE FOR A FUEL CELL COMPRISING: A CATALYTIC LAYER CONTAINING A MIXTURE OF A CATALYST AND OF A POLYMER, A STOP LAYER ARRANGED ON ONE OF THE FACES OF THE CATALYTIC LAYER AND CONSISTING ESSENTIALLY OF SAID POLYMER, THE STOP LAYER AND THE CATALYTIC LAYER HAVING AN OPEN POROSITY OF FROM ABOUT 40 TO ABOUT 60%, AND CURRENT COLLECTOR MEANS MADE OF AN ELECTRONICALLY CONDUCTIVE AND CHEMICALLY INERT MATEIAL, SAID ELECTRODE BEING CHARACTERIZED IN THAT THE CURRENT COLLECTOR MEANS CROSSES THROUGH PORTIONS OF THE WHOLE OF THE STOP LAYER AND PENETRATES INTO PORTIONS OF THE CATALYTIC LAYER
 2. The electrode of claim 1, further comprising a separator layer comprising a fibrous tissue arranged on the other face of the catalytic layer.
 3. The electrode of claim 1, wherein said current collector means is a reticulated member having a plurality of interconnected portions that extend through said stop layer into said catalytic layer.
 4. The electrode of claim 1, wherein said collector means is a metallic grid having a plurality of elements spaced from each other in a predetermined pattern that extend through said stop layer into said catalytic layer.
 5. The electrode of claim 4, wherein said grid is made of two sets of parallel extending metallic elements, which intersect each other.
 6. The electrode of claim 4, wherein the grid is made of nickel or stainless steel.
 7. The electrode of claim 1, wherein the polymer is a polyfluorinated polyolefin.
 8. The electrode of claim 1, wherein the catalyst is powdered active carbon and said polymer is polytetrafluorethylene.
 9. The electrode of claim 1, wherein the collector means penetrates into said catalytic layer with an outer surface that is level with and that forms a portion of an outer surface of one face of the electrode and an inner surface that contacts portions of the stop layer disposed within said electrode, other portions of said stop layer forming the remaining portions of the outer surface of said one face of the electrode.
 10. The electrode of claim 1, wherein the catalytic layer is a sintered porous member.
 11. A method for preparing a porous electrode for a fuel cell which comprises: a. depositing a mixture of a catalyst in a proportion by weight comprised between about 90 and about 40% and of a polymer in a proportion by weight comprised between about 10 and about 60%, dispersed in a liquid volatile diluent, on a metal sheet; b. partial drying the deposit; c. depositing a stop layer consisting essentially of said polymer diluted in the liquid diluent on the catalytic layer; d. drying of the stop layer; e. arranging a current collector means on the stop layer and compressing the collector means at a pressure from about 500 to about 2,500 kg/sq. cm to form an assembly of layers and collector means; and f. sintering of the assembly by heating at an elevated temperature.
 12. The method of claim 11, wherein the catalyst is active carbon and the polymer is a polyfluorinated polyolefin.
 13. The method of claim 12, wherein the polymer is polytetrafluorethylene.
 14. The method of claim 13, wherein the assembly is sintered in a neutral or reducing atmosphere at a temperature of from about 350*C. to about 420*C. for about 5 to about 60 minutes.
 15. The method of claim 11, wherein said diluent is dibutylphthalate.
 16. The method of claim 11, wherein a lubricant is used jointly with the diluent.
 17. The method of claim 16, wherein the lubricant is a fluorocarbon oil.
 18. The method of claim 1, wherein the metal sheet is aluminum.
 19. An electrochemical storage cell comprising at least one electrode according to claim
 1. 20. The electrode of claim 1, wherein the stop layer consists of polytetrafluorethylene.
 21. The electrode of claim 1, wherein the stop layer is free of catalyst.
 22. A method of claim 11, wherein said stop layer consists of polytetrafluorethylene diluted in dibutylphthalate.
 23. The method of claim 11, wherein the stop layer is free of catalyst. 